Radio frequency coupling network



Dec. 11, 1945. e. w. KLINGAMAN RADIO FREQUENCY COUPLING NETWORK Fi'llaiiyu I Zmventor attorney;

' resonant characteristics.

Patented Dec. 11, 1945 RADIO FREQUENCY COUPLING NETWORK I George W. Klingaman, Lynnport, Pa; asslgnor to Radio Corporation Delaware of America, a corporation of Application August 17, 1943, Serial No. 499,018

v v 6 Claims. This invention relates generally to signal transmission circuits and more particularly to radio frequency coupling networks which mayv I be tuned over a predetermined frequency band for coupling a variable frequency power source to a load circuit.

Coaxial transmission lines are used extensive ly in coupling radio frequency generators to' load circuits such as, for example, antenna arrays, etc. It is often desirable to' provide coupling networks which may be tuned to provide effective transmission of power at predetermined points within a relatively wide frequency band. Coaxial transmission lines may be employed'to provide distributed circuit constants in such networks, but frequentlydifllculty is encountered in tuning the coaxial line to provide the required Heretofore, tuning of coaxial transmission lines has usuallyinvolved slotting of the outer conductor to provide for adjustable connections to the inner transmission line conductor.

The instant invention comprises an improvement upon existing coaxial transmission line networks,- in that adJustment over a relatively wide band of frequencies may be effected by changing the position of a single adjustable eonneetion between the outer conductors of two adjacently disposed coaxial lines. Briefly a typi-' cal embodiment of the invention includes a conventional coaxial line which is coupled aperiodically to a radio frequency generating source. The outer conductor of the coaxial line is coninterdependent with the characteristics of the,

load and the input circuit to the second and third coaxial lines.

Among the objects ofthe invention are to provide an improved method of and means for coupling a source of radio frequency energy to a load circuit. Another object of the invention is'to provide an improved coupling network for connecting a source of radio frequency energy to a load circuit wherein the source is aperiodically coupled to a first transmission line, and second and third coaxial transmission lines are connected between the first transmission line and the load circuit in a manner to provide afilter network including an adjustable inductive elemerit serially connected between the source and dio frequency energy to a load circuit, wherein.

the coupling network may be tuned over a 'pre-' determined frequency. band. An additional object of the invention is to provide an improved coupling network for. connecting a radio frequency source to a load circuit wherein the coupling network may be tuned to a predetermined,

mean frequency and the band-pass characteristics of the circuit may be adjusted within predenected to one terminal of the load circuit and also is connected to the inner conductor of a second coaxial line. The inner conductor of the first coaxial line is connected to the outer conductor of the second coaxial line. A third coaxial transmission line, preferably disposed adjacent and parallel to the second coaxial line, has its inner conductor connected to the remaining terminal of the load circuit; Anadiustable connection is made between suitable points on the outer conductors of the second and third coaxial lines to provide tuning of the coupling network.

The coupling network has a conventional single resonance characteristic if the adjustable connection provides for equal portions of the between the outer conductors of these lines. In 4 either instancathe resonant characteristics are termined limits. a

The invention will be further described by reference to the accompanying drawing of which Figure l is a schematic circuit diagram of the basic circuit and Figure 2 is a schematic circuit diagram of a preferred practical embodiment thereof. plied to similar elements throughout the drawing.

Referring to Figure 1, the basic transmission circuit comprises a source of radio frequency energy e which is coupled aperiodically through a series impedance Zi to one terminal of a variable tapped inductive element comprising the portions Ll, L2. The remaining terminal of the inductive element L2 is connected through a coupling capacitor C2 to one terminal of a load device which is represented as'an impedance 21. A tapped point on the variable inductor Ll, L2

is connected through a second capacitor CI to the remaining terminal of the load impedance Z1, and to the remaining terminal of the radio frequency source e. I

It will be seen that if the portions Ll, L2 of the variable inductor are equal andthe capacitorsCl C2- are equal, that the transmission char- Similar reference characters are apbe bi-resonant and provide for reflective tre mission line e which corresponds to the series oi said network.

coaxial line 8 has its r conductor connec said our. capacitive means to the 2 v oneness pacitor (it is connected. then the network mission within a limited frequency hand. The ur conductors of the second and third ooamal mean frequency response of the circuit y he r adjusted by varying the total amount of the 5 asinventionr inductance of the portions Li, L2. 1. A transmission network. for coupling a source ,Figure 2 illustrates a practical embodiment of or radio frequency energy to a l circuit comthe basic circuit described in Figure 1 wherein 9-":143 a series tuned circuit including a first coaxial transmission lines are employed as the fixed capacitor and a tapped variable inductor, basic circuit components. The r of 1o aperiodic means and said series tuned circuit sefrequency energy e is represented as the anode rialiy connecting said source and said iced circlrcuit of a thermionic tube 8 which includes a cult, a second fixed capacitor shunting a portion parallel resonant tank circuit comprising a first or said series tuned circuit and said load circuit, inductor 2 and capacitor 8. A second inductor t and w i'or amustins the portion of said series is coupled apericdically to a t inductor 2, and is "tuned circuit shunted by said second cacitor is connected to one end of a'iirst coaxial trans to v.1"? the frequency band-ow characteristics impedance Z! oi the basic circuit. The outer 2. A or: circuit for conductor of the first coaxial transmission line t or radio freq ency energy to a load circuit coinis connected to the inner conductor of a second -21) aperiodic means for deriving er from coaxial transmission line 8, and to one terminal said source, variable inductive means, first fixed of the load device i which corresponds to the iced capacitive mmns, second fixed caitive means impedance 21 of the basic circuit. The as conand means for connecting to a load circuit, means ductor of the first coaxial trission line is seri connecting said e, said aperiodic connected to the outer conductor of the second $5 "m said inductive means, and said first ca-' coaxial line i. pecitive means to one terminai of said load con- A th rd om tr m d p nectins means, means serially connecting an injscent to, and preferably parallel to, the second termediate point on said inductive n1e== :-v

. l- 'a g #121" of said 1 connecting means and said to the remaining terminal of the load device 7. te An adjustable connection 9 is internosed between source, means for changing said intermedithe outer conductors of the second and third coate connection to said inductive to vary axial transmission lines t, 8, respectively. the iency band-pass c reristics of said The length of the outer conductor of the secnetwork's. v 0nd transmission 11118, 5 between the connection 35 3, A m we ion network foi coupling gsuurce to the load device i and the ustabie connecof radio r equency energy to a circuit co n-- tion t corr spo s to the portion M of th r rpg a pair or concentric transmission lines iahle inductor oi the basiccircuit. Sly, the each, having coexinily disposed; inner and o ter portion of the third coaxial line between the edconductors, means for connecting adjacent ends through iustable connectiont and the 1- ns connecso of said r conductors of said lines to difierent' 1 to the 1 r device comespimds t the W terminals of said load circuit, a third transmistion L2 of the variable inductor. The capaci aperiodic means for connecting tance between the conductors oi the second t to said source, means connecting the conductors mission line it is represented y the fi i G5 or said third line to separate conductors oi one which is shown in lines within the tr slim line- Simi y, the cii w bcwewihe means connecting the outer conductors of said conductors oi the third coamal on line 3x2. 0! lines to vary the uctance in said tii is represented by the capacitor or indicaiw by dash lines within the transon line.

1 on network for coupli Source Adjustment of the position of the cction it sog mm icy energy to a load circuit combetween the outer conductors oi the second and ':.::'j mof open-ended n nm t third coaxial l ffl lines ionsitudiill-Ins" each having coasially disposed inner Rally ne the lines provides r 8 1% i the and outer conductors, for connecting odtotal inductance provid d by the uctive p riecent ends of said r conductors of mid lines .tions Li, L2. lithe connection t is red uni- 1s t sm a; t pf said load t, a .2 formly along both of the m lin concentric ms the network will provide a i ductive m for connecting to said source, onance. If, however, the ecticn is non-uniformly, as indicated by the dash 122- 8', difierent proportionate amounts oi the inductive mes. and .ammame me com elements Li, L2 will be incl in t WWW? nee the outer conductors of said pair 0!. linm there y Providing a biiiito r the inductance in said network. acteristic which y be an to fi d. w

is. line having aperiodic lnhis or the-tyne described in claim 8 quencies over a limited ire-cu bdcd in that adjustment or said adjust It will beswnthat adiusen or both oi the @518 m tuning and the lc tiv w 0f I iii of the inductance oi each of saidconcem network may be 3mm trio uctors insaid network. oi the connection or the tor to prede termined points on the outer conductors oi I second and third'co um.-

ii. 8. Calculation of the actual circui ":1 ts rsili in that adjustment of saidcdj .tions' oi I e inductance or each or said concentrio ccnducmrs in network.

provides insertion of equal properl of the t described in claims.

provides rtion of unequal ipropor- 

